Bubble bursts;Letter

15th May 1998 at 01:00
I very much enjoyed Ted Wragg's article entitled "Bursting with ideas" in TES Primary magazine on April 24. I shall certainly be trying out his bubble-making ideas this summer with my children.

However, I think some of the physics was wrong. The colours on bubbles are caused by interference, not refraction. Also the bubbles do not sink because water drains to the bottom. They sink because their weight is greater than the upthrust they experience (the redistribution of water in the bubble does not change its weight).

We experience upthrust when we float in water: it is equal and opposite to our weight. The draining of water to the bottom of the bubble changes the thickness of the soap film, and it is this that causes the coloured patterns to move across the bubble. The thinning of the soap bubble eventually causes it to appear black and burst.

Ted says: "At this early age the physical universe can be incredibly exciting." I still think it is!

John Williams Head of science New Hall School Chelmsford

Log-in as an existing print or digital subscriber

Forgotten your subscriber ID?


To access this content and the full TES archive, subscribe now.

View subscriber offers


Get TES online and delivered to your door – for less than the price of a coffee

Save 33% off the cover price with this great subscription offer. Every copy delivered to your door by first-class post, plus full access to TES online and the TES app for just £1.90 per week.
Subscribers also enjoy a range of fantastic offers and benefits worth over £270:

  • Discounts off TES Institute courses
  • Access over 200,000 articles in the TES online archive
  • Free Tastecard membership worth £79.99
  • Discounts with Zipcar, Buyagift.com, Virgin Wines and other partners
Order your low-cost subscription today